The present invention generally pertains to a process of population screening that leads to the detection of Lysosomal Storage Disorders (“LSDs”) and related diseases in a subject. More particularly, this invention pertains to compounds, reagents, and methods for identifying and quantifying the levels and ratios of multiple target antigens that are used to identify individuals likely to be affect with an LSD. The target antigens are naturally present in biological fluids or tissues of either LSD or non-LSD patients.
LSDs represent a group of over 40 distinct genetic diseases that generally affect young children. Individuals that are affected with a LSD present a wide range of clinical symptoms that depend upon the specific disorder or a particular genotype involved. The clinical symptoms associated with LSD's can have a devastating impact on both the child and the family of affected individuals. For example, central nervous system dysfunction, behavioral problems, and severe mental retardation are characteristic of many LSDs. Other clinical symptoms may include skeletal abnormalities, organomegaly, corneal clouding and dysmorphic features (Neufeld and Muenzer, 1995). Patients are usually born without the visible features of a LSD, but early stage symptoms can quickly develop into a progressive clinical concern. In severe cases, the affected children require constant medical management but still often die before adolescence.
The significance of LSDs to health care becomes obvious when comparing the group incidence rate for a LSD (1:5,000 births) to the group incidence rate of other with well-known and intensively studied genetic disorders, such as phenylketonuria (1:14,000) and cystic fibrosis (1:2,500), wherein these figures reflect incidence rates for Caucasian populations.
Once an individual begins to present the symptoms of a LSD, the actual clinical diagnosis of the disease is still a complex process. A clinical diagnosis of a LSD often requires multiple visits to a range of specialists, which can take months or even years. This long process is extremely stressful on the patient and family. Fortunately, there has been considerable progress in the diagnosis of LSDs over the past 20 years. For example, the development and introduction of chromatographic-based urine screens for a specific group of LSDs called mucopolysaccharidoses (“MPS”) and oligosaccharidoses has facilitated screening of clinically selected patients for these disorders. Following a clinical index of suspicion for the disorders, the next stage of diagnosis involves a urine screen, wherein a “positive” urine screen is then followed by specific enzymatic analysis. Although the chromatographic-based screening methods are simple to perform, they are relatively labor-intensive and often require experience to accurately interpret results. One example includes a method of identifying and quantitating biochemical markers (“biomarkers”) that are present in biological fluids or tissues of a patient having a MPS or related disorders comprises determining a target quantity of a target MPS biomarker oligosaccharide from a target biological sample taken from the target animal, and then comparing the target quantity to a reference quantity of a reference MPS biomarker oligosaccharide for the diagnosis, characterization, monitoring, and clinical management of MPS and related disease, as described in PCT Application AU03/00731 entitled “Identification of Oligosaccharides and their Use in the Diagnosis and Evaluation of Mucopolysaccharidoses and Other Related Disorders,” filed on Jun. 13, 2003 with Hopwood et al., listed as inventors (the entire content of PCT Application AU03/00731 is hereby incorporated by reference). Consequently, chromatographic-based screening tests for LSDs are not used in some centers. Furthermore, these chromatographic-based screens are not readily amenable to automation, which has further limited their utilization in screening strategies for newborns.
The production of specific substrates and antibody capture assays has made the enzymatic analyses for LSDs more accurate. Although not wanting to be bound by theory, the majority of LSDs result from a reduction in levels of a particular enzyme(s) involved in a specific LSD, and the identification of the specific enzyme(s) steady state in normal individuals will help identify the particular form of LSD in the affected individual. The ability to quickly and accurately determine the levels of the more than 40 enzymes known to be involved with LSDs will assist in the development of better and more economical screening assays. Unfortunately, many of the chromatographic-based screens and enzyme assays mentioned above are time-consuming, invasive, complex, and require cultured cells, or tissue biopsies, which tends to make such assays inconvenient and expensive. As a result, testing for a LSD is often not a first line strategy for an affected child with early stage symptoms. Newborn screening for LSDs promises to provide early detection of the LSD, but all newborns must be screened in order to detect the disease early. Patients having a family history of LSDs may have a justifiable reason to perform an early screen for a LSD. However, the cost of an early screen of the LSD in individuals not having a family history may not be justified economically. Therefore, it would be beneficial that any LSD screening process be capable of economically screening large numbers of newborns.
One common feature of LSDs is the accumulation and storage of materials within lysosomes. It is generally recognized that the accumulation and storage of material in LSD affected individuals results in an increase in the number and the size of lysosomes within a cell from approximately 1% to as much as 50% of total cellular volume. In non-affected individuals, such materials are typically degraded into degradation products within the lysosome and then transported across the lysosomal membrane. Certain lysosomal proteins are present at elevated levels in the lysosomes of affected individuals (Meikle et al., 1997; Hua et al., 1998). These identified proteins are useful biomarkers for an early diagnosis of all LSDs. For example, sensitive immunoquantification assays have been developed to monitor the level of useful biomarkers such as the lysosome-associated membrane proteins (“LAMPs”), saposins, and α-glucosidase. Although the determination of either LAMP-1 or LAMP-2 levels alone in an ‘at-increased-risk’ group will identify up to 65% of LSD affected individuals, the combination of a LAMP with one of the saposins increase identification of LSD affected individuals to approximately 85%. Therefore, a method to identify two or more biomarkers simultaneously would increase the accuracy of diagnosing a specific LSD as compared to any single assay. An automated multiplex assay that could perform a simultaneous screen on each of the known LSD deficient enzymes would reduce time and cost for accurate LSD diagnosis.
Multiplexing Bead Technology is built around 3 core technologies. The first is the family of fluorescently dyed microspheres having specific biomolecules bound to the surface of the microsphere. The second is a flow cytometer with 2 lasers and associated optics to measure biochemical reactions that occur on the surface of the microspheres, and the third is a high-speed digital signal processor to efficiently manage the fluorescent output. This type of system has been described in, for example: U.S. Pat. Nos. 6,449,562; 6,524,793 and U.S. patent application Ser. No. 09/956,857. U.S. Pat. No. 6,449,562 (“the '562 Patent”) entitled “Multiplexed Analysis of Clinical Specimens Apparatus and Method,” having Chandler et al. listed as inventors was issued on Sep. 10, 2002. The '562 Patent discloses a method for the multiplexed diagnostic and genetic analysis of enzymes, DNA fragments, antibodies, and other biomolecules comprising the steps of constructing an appropriately labeled beadset, exposing the beadset to a clinical sample, and analyzing the combined sample/beadset by flow cytometry. Flow cytometric measurements are used to classify, in real-time, beads within an exposed beadset and textual explanations, based on the accumulated data obtained during real-time analysis, are generated for the user. The inventive technology of the '562 Patent enables the simultaneous, and automated, detection and interpretation of multiple biomolecules or DNA sequences in real-time while also reducing the cost of performing diagnostic and genetic assays. However, the '562 Patent does not describe how to utilize the technology for diagnosing LSD's.
U.S. Pat. No. 6,524,793 (“the '793 Patent”) entitled “Multiplexed Analysis of Clinical Specimens Apparatus and Method,” having Chandler et al. listed as inventors, was issued on Feb. 25, 2003. The '793 Patent discloses a method for the multiplexed diagnostic and genetic analysis of enzymes, DNA fragments, antibodies, and other biomolecules comprising the steps of constructing an appropriately labeled beadset, exposing the beadset to a clinical sample, and analyzing the combined sample/beadset by flow cytometry. Flow cytometric measurements are used to classify, in real-time, beads within an exposed beadset and textual explanations, based on the accumulated data obtained during real-time analysis, are generated for the user. The '793 Patent enables the simultaneous, and automated, detection and interpretation of multiple biomolecules or DNA sequences in real-time while also reducing the cost of performing diagnostic and genetic assays. However, the '793 Patent does not describe how to utilize the technology for diagnosing LSD's.
U.S. patent application Ser. No. 09/956,857 (“the '857 Application”) entitled “Multiple Reporter Read-out for Bioassays” was published on Mar. 20, 2003. The '857 Application describes a method for detecting a plurality of reactive sites on an analyte, comprising allowing reactants on an addressable microsphere and the reactive sites to react, forming reactant-reactive site pairs distinguishable by fluorescence intensity. The '857 Application also provides a method for detecting a plurality of analytes in a sample using addressable microspheres in combination with one or more reporter reagents. Also provided is a method for determining allele zygosity of a genetic locus having two alleles or more alleles using microparticles, and a method for detecting a plurality of SNPs in nucleic acid molecules. The '857 Application also provides a composition comprising an addressable microsphere carrying at least two fluorescent reactants capable of forming reactant-analyte pairs distinguishable by their fluorescence intensity, and kits comprising the inventive composition and a plurality of reporter reagents. However, the '857 Application does not describe how to utilize the technology for diagnosing LSD's. The entirety of each of the applications or patents listed above is hereby specifically incorporated by reference.
Accordingly, there is a need for the development of a fast, accurate and economical screen for early diagnosis of LSDs, which is amenable to automation. The ability to identify specific LSD enzymes in an automated multiplex assay will have a significant impact on the development of a newborn screening programs, as well as the ability to address a number of other issues associated with the early diagnosis and treatment of LSDs. The present invention provides compounds, reagents, and methods for a LSD diagnostic multiplex assay.